Twin brothers, Billy and Bobby, can mow their grandparent's lawn in 76 minutes. Billy could mow the lawn by himself in 15 minutes less time than it would take Bobby. How long would it take Bobby to mow the lawn by himself?

Question

amistre64 · Answer

T(bob) + T(bill) = 76  is what im thinking

amistre64 · Answer

bob-15 + bob = 76

amistre64 · Answer

2bob = 91

bob = 91/2 = 45.5 maybe

amistre64 · Answer

that almost feels right; almost ...

amistre64 · Answer

the by himself part is not being taken into account

anonymous · Answer

amistre 64  ineed ur help

amistre64 · Answer

I dont know c++

anonymous · Answer

oh....ok...:(

amistre64 · Answer

if we had the set up the we know bob and bill alone we could get to time together .... so im gonna have to look backwards at this :)

amistre64 · Answer

bob = time (b) alone
bill = time (b -15) alone
$$\frac{1}{b}+\frac{1}{b-15}=\frac{1}{76}$$
$$\frac{b-15}{b(b-15)}+\frac{b}{b(b-15)}=\frac{1}{76}$$
$$\frac{b-15+b}{b(b-15)}=\frac{1}{76}$$
$$\frac{b(b-15)}{b-15+b}=76$$
$$\frac{b^2-15b}{2b-15}=76$$
$$b^2-15b=76(2b-15)$$
$$b^2-15b-76(2b-15)=0$$
$$b^2-15b-152b+1140=0$$
$$b^2-167b+1140=0$$
maybe?

amistre64 · Answer

b = about 160 or 8; so id go with 160 minutes as a gut thing

if:$$\frac{1}{160}+\frac{1}{160-15}=\frac{1}{76}$$then it should be good

amistre64 · Answer

http://www.wolframalpha.com/input/?i=1%2F160+%2B+1%2F%28160-15%29+-+1%2F76 yeah, im going with that, or close to it